The present invention relates to detecting a change between images, such as for object detection or tracking in video surveillance, for scene change detection, for psycho-optical adaptation of the data rate/quality ratio of encoded video streams, for efficient storage of video data, for noise reduction or the like.
An important step in processing video sequences is detecting changes from one image to the next and thereby frequently also the allocation of the changes to a specific image region. From that, further processing steps, such as for object detection and tracking can be controlled.
With the increasingly rising resolution of images, transmission or storage of video sequences is frequently only feasible in a compressed form. This significantly saves necessitated transmission rate via radio or cable, storage space and also data rate when loading or storing files. A frequently used standard for these applications is, for example, JPEG2000. The same offers advantages at high image qualities and offers a very flexible access to image parts, sometimes also referred to as scalability. When only a section of an image is necessitated, then decompression for part of the image is possible with significantly reduced computing effort.
For performing detection of changes, however, it has so far not been necessitated to completely decompress the images at first. Only then, an algorithm for detecting changes based on the decoded image points or pixels can be applied. An evaluation of which image region is necessitated is so far not possible prior to decoding. In particular in high-resolution and compressed images, such as JPEG2000 images, this necessitates a lot of computing time.
As has already been mentioned, for detecting changes in image sequences, it is possible to completely decompress the entire image material. This is shown in FIG. 9. Images of a sequence of images 904 from an image capturing apparatus 902 are individually encoded into a sequence of encoded images 908 by a JPEG2000 encoder 906, i.e., every image separately in a self-contained manner and independent of other images, and are then subject to change detection in a block 910, wherein this block, however, comprises a JPEG2000 decoder 912 to again completely decode every image of the incoming sequence 908 of encoded images to obtain a reconstruction 914 of the sequence of images 904, on which again a sub block 916 of the change detection block 910 performs pixel-based change detection between subsequent images to output the result, i.e. the detected changes 918, at a subsequent further processing block 920. The algorithms that can be used for pixel-based change detection in block 916 for determining a detection of amended regions are described, for example, in T. Aach and A. Kaup: Bayesian algorithms for change detection in image sequences using Markov random fields. Signal Processing: Image Communication, 7: 147-160, 1995. In the case of compressed and high-resolution encoded sequences 908, real time processing in change detection 910 is hardly possible. An alternative is performing change detection 910 only after storing the encoded image material 908. However, in this case the search for changes in the stored image material necessitates a lot of computing time. Offline processing of a stored version of the image material with full resolution is problematic due to the necessitated storage space as well as the occurring latency times during storing or during storage accesses.
Thus, a more efficient detection of changes between images would be desirable.